Heat shields are used for example in combustion chambers or flame tubes, which may be part of a kiln, a hot gas duct or a gas turbine and in which a hot medium is generated or conveyed. For example a combustion chamber that is subject to a high level of thermal loading can be lined with a heat shield to protect it from excessive thermal strain. The heat shield typically has a number of heat shield elements arranged to provide a high level of coverage, which screen the walls of the combustion chamber from the hot medium, e.g. a hot combustion gas, and thereby counteract any excessive thermal loading of the combustion chamber wall.
Such a ceramic heat shield is for example disclosed in EP 0 558 540 B1. It comprises a number of square ceramic heat shield elements, which are attached to an axially symmetrical support structure of the flame tube. Each heat shield element has a hot side facing the hot medium, a cold side facing the supporting wall and four peripheral surfaces connecting the hot side to the cold side, the two peripheral surfaces of a heat shield element opposite each other in the peripheral direction of the support structure being provided with grooves. Spring-type clamps engaging in the grooves serve to fix the heat shield elements in the peripheral direction of the support structure, leaving a gap in between. To keep the thermal loading of the support structure as low as possible, a cooling fluid is fed to the gaps between the heat shield elements, flowing from the cold side towards the hot side through the gap, therefore blocking the gap to prevent penetration of the hot medium.
A ceramic heat shield that is particularly suitable for lining a flame tube for a gas turbine is disclosed for example in DE 41 14 768 A1. It comprises a number of square or trapezoidal ceramic heat shield elements, which are attached to a supporting wall of the flame tube. Each heat shield element has a hot side facing the hot medium, a cold side facing the supporting wall and four peripheral surfaces connecting the hot side to the cold side, two peripheral surfaces on opposite sides of a heat shield element being provided with grooves. Retaining elements with clamp sections are used to attach the heat shield elements to the supporting wall, engaging in the grooves in the peripheral surfaces and clamping the heat shield element in one direction. The retaining elements also each have a support section to support a heat shield element against a third peripheral surface. On the hot side this third peripheral surface has a projection projecting beyond the remainder of the peripheral surface, which rests on the support section of the retaining element such that the heat shield element is also secured in a direction perpendicular to the clamping direction. To allow thermal expansion of the heat shield elements, when they are exposed to the hot medium, the heat shield elements are arranged such that small gaps remain between them. With the fixing method disclosed in DE 41 14 768 A1 the heat shield elements are arranged at defined positions on the supporting wall.
A combustion chamber lining with heat shield elements is also disclosed in EP 1 302 723 A1. In this combustion chamber lining sealing elements are arranged in the gaps between the heat shield elements. The heat shield elements of this combustion chamber lining have grooves on their peripheral surfaces. A sealing element arranged in the gap between two heat shield elements thereby engages in the grooves in the two peripheral surfaces bounding the gap.